βαρρ
TABLE OF CONTENTS
Geology
and Basin Analysis of
Western
Offshore Libya
(Blocks
O1, O2, O3, O4, O14, O15, O16 and NC41)
VOLUME ONE
Subject Page
Table
of Contents and List of Figures i
1. INTRODUCTION
1.1 Background to the project 1
1.2 Location of the study area 3
1.3 History of previous research 4
1.4
History of hydrocarbon exploration 8
A) Elf-Aquitane company activities and
results 8
B) Esso and Sirte Oil Company activities
and results 9
C) Agip company activities and
results 9
D) Total activities and results 10
1.5 Nature of database 11
1.6 Methodology 12
A) Geophysical method 13
B) Geological methods 14
2.STRATIGRAPHY OF TRIPOLI-GABES BASIN
2.1 Introduction 16
2.2 Chronostratigraphy 18
2.3 Stratigraphy of the basin 19
2.3.1
Al-Azizyah Formation 19
2.3.2
Abu-Shaybah Formation 20
2.3.3
Abu-Ghaylan Formation 21
2.3.4
Bir Al-Ghanam Formation 22
2.3.5
Kiklah Formation 23
2.3.6
Zebbag Formation 25
2.3.7 Kef Formation 26
2.3.8
Abiod Formation 27
2.3.9
El-Haria Formation 29
2.3.10 Metlaoui Group 30
2.3.10.1 Chouabine Formation 32
2.3.10.2 Jirani Dolomite
Formation 33
2.3.10.3 Faid Formation 34
2.3.10.4 Tajoura Formation 35
2.3.10.5 El-Garia Formation 36
2.3.10.6 Bou-Dabbous
Formation 37
2.3.11 Cherahil Formation 38
A) Cherahil “A” Member 39
B) Reineche Member 40
C) Cherahil “B” Member 40
2.3.12 Souar Formation 41
2.3.13 Salambo and Ketatna Formation 42
2.3.14 Mahmoud Formation 43
2.3.15 Melqart Formation 44
2.3.16 Oued Bel Khedim Formation 45
2.3.17 Raf-Raf and Segui
Formations 46
2.4 General comments on the stratigraphy of
Sirte Basin 47
3. REGIONAL TECTONIC FRAMEWORK
3.1 Introduction 49
3.2 From Tethys to Mediterranean (Plate tectonic
model) 51
I) Lias
(Pliensbachian), 190 Ma 53
II) Late Jurassic (Callovian), 155
Ma 54
III) Jurassic-Cretaceouَ boundary,
130 Ma 55
IV) Middle Cretaceous (Aptian), 110
Ma 56
V) Latه Cretaceous
(Santonian-Campanian),80 Ma 57
VI)
Cretaceous-Paleocene boundary, 65 Ma 58
VII) Late Eocene
(Priabonian)-Oligocene 35 Ma 59
IIX) Early Miocene (Aquitanian), 20
Ma 60
IX) Middle Miocene (Tortonian), 10
Ma 62
X) Present 63
3.3 Physiography and topography of the
Mediterranean 63
3.4 Geologic and tectonic setting of the
Mediterranean
Basin 65
3.5 Regional
geology and tectonic
setting of the
Pelagian Platforf 67
3.5.1 Introduction 67
3.5.2
Physiography and bathymetry 67
3.5.3
The geodynamic evolution 68
4.DATABASE DESCRIPTION
4.1 Introduction 79
4A: PETROGRAPHY
4.2 Methods and technique 79
4.2.1
Methods and procedure 79
4.2.2 Techniques and microscope 80
4.3
Microfacies description 81
4.3.1 The Zebbag Formation 81
4.3.2
The Kef Formation 83
4.3.3
The Abiod Formation 84
4.3.4 The El-Haria
Formation
85
4.3.4.1 The El-Haria 'A' 85
4.3.4.2 The El-Haria 'B' 87
4.3.5
The Metlaoui Group 88
4.3.5.1 Chouabine Formation 88
4.3.5.2 Jirani Dolomite
Formation 93
4.3.5.3 El-Garia Formation 97
4.3.6 Cherahil Formation 110
4.3.6.1 Cherahil 'A' Member 110
4.3.6.2 Reineche Member 113
4.3.6.3 Cherahil 'B' Member 116
4.3.7
Souar Formation 118
4B: DATA DESCRIPTION
4.4 Description of the geological and
geophysical data 120
4.4.1
Introduction 120
4.4.2
Subsurface geological maps and sections 122
4.4.2.1 The Zebbag Formation 122
4.4.2.2 The Kef Formation 123
4.4.2.3 The Abiod Formation 125
4.4.2.4 The El-Haria Formation 126
4.4.2.4.1 The El-Haria
'A' Member 126
4.4.2.4.2 The El-Haria 'B' Member 127
4.4.2.5 The Metlaoui Group 128
4.4.2.5.1 The Chouabine
Formation 130
A-Dolomitic wackestone facies 131
B-Oolitic
packstone-grainstone
facies 131
C-Lithoclast-bioclast
mudstone
facies 132
4.4.2.5.2 The Jirani Dolomite Formation 133
A-Anhydritic dolomite
and
dolomitic mudstone
facies 133
B-Dolomite and dolomitic
limestone facies 134
4.4.2.5.3 The El-Garia Formation 135
4.4.2.6 The Cherahil and Souar Formation 138
4.4.3
GRAVITY AND MAGNETIC MAPS OF THE BASIN 143
´.4.3.1 The Gravity Aspect 143
4.4.3.2 The Magnetic Aspect 144
4.4.4
DESCRIPTION OF THE MULTICHANNEL SEISMIC DATA 146
4.4.4.1 Line WT-84-28 149
4.4.4.2 Line WT 84-10 153
4.4.4.3 Line WT 84-30 158
4.4.4.4 Line RS-86-01 161
4.4.5
DESCRIPTION OF THE STRUCTURAL MAPS 164
4.4.5.1 The structure map of base Tertiary 165
4.4.5.2 The structure map of Lower Eocene 166
5. SUBSIDENCE HISTORY AND CRUSTAL
EXTENSION MODELS
5.1 Introduction 168
5.2 Subsidence overview 169
5.3 Burial history analysis 171
5.4 Compaction 173
5.5 Correction for compaction (technique and
method) 175
5.6 The Backstripping procedurs 179
A) Water depth 179
B) Sea level 181
5.7 Tectonic subsidence 184
5.8 Basement subsidence 189
5.9 Subsidence curves 191
5.10
Subsidence maps 193
5.10.1
Basement subsidence rate maps 193
5.10.2
Cumulative basement subsidence maps 196
5.11
Observations and prediction 197
6. THERMAL MATURATION HISTORY OF
TRIPOLI-GABES BASIN
6.1 Introduction 200
6.2 Geothermal gradient of the basin 200
6.3 Maturation of organic matter 203
6.4 Measured maturities (TAI) 205
6.5 The Lopatin method and predicted
maturity 206
6.6 Calibration of the calculated (predicted)
maturities 208
6.7 Observed and predicted maturity 211
6.7.1
Source rock potential of the Abiod Fm. 212
6.7.2
Source rock potential of the El-Haria Fm. 213
6.7.3
Source rock potential of the Metlaoui Group 214
6.8 Summary 216
7. AN OVERVIEW OF THE MESOZOIC EVAPORITES
7.± Background data on evaporites 218
7.2 Physical properties of salt rock and
terminology 219
7.3 The evaporitic basin and models of
deposition 221
7.4 The Early Mesozoic evaporites of Tripoli-
Gabes Basin 224
7.5 Genesis of the salt structures 226
7.6 Salt structures in the Tripoli-Gabes
Basin 229
7.7 The age determination of salt movement 230
7.8 Genesis of salt deformation in the Tripoli-
Gabes Basin 231
A) Basinal configuration 231
B) Overburden loading (halokinesis) 232
C) Tectonics 233
8. THE GEOLOGY OF THE EARLY
TERTIARY SEQUENCES
8.1 Introduction 235
8.2 Sedimentology of the El-Haria Formation 236
A) The Maastrichtian El-Haria Member 238
B) The Paleocene El-Haria Member 239
8.3 Sedimentology of the Metlaoui Group 241
8.3.1
Introduction 241
8.3.2
Sedimentology of the Chouabine Formation 242
A) Dolomitic wackestone facies 243
B) Oolitic packstone-grainstone
facies 244
C) Lithoclast-bioclast mudstone
facies 245
8.3.2.1 Diagenesis of the Chouabine
Formation 246
8.3.3
Sedimentology of the Jirani Dolomite 247
8.3.3.1 Origin of the Jirani
Dolomite 249
8.3.4
Sedimentology of the El-Garia Formation 251
8.3.4.1 Diagenesis of the El-Garia Formation 257
A) The marine phreatic
environment 257
B) Near-surface meteoric
environments 259
C) Burial (subsurface)
diagenesis 261
8.3.4.2 Conclusion 263
9.DISCUSSION, SUMMARY, CONCLUSIONS
AND RECOMMENDATIONS
9.1 General Discussion 264
9.2 Summary and Conclusion 269
9.3 Recommended Future Work 271
10.REFERENCES
11.APPENDICES
Fig 1.1 Location map showing the
study area relative to the Pelagian Platform.
Fig 1.2 Map of both on land and
offshore northwestern Libya showing Concession
Blocks (for offshore operators see text).
Fig 1.3 Seismic grid map showing
coverage obtained by Agip (N.A.M.E) in Block NC-41.
Fig 1.4 Location map of wells
drilled by the various companies (see text for details of each well).
Fig 1.5 Regional seismic lines
employed in this study (coloured lines indicate seismic profiles included in
the report).
Fig 1.6 Key to lithologic symbols
and abbreviations used throughout the report.
Table 1.1 List of well logs used in
the study area.
Table 1.2 List of seismic lines
provided for this study.
Table 1.3 List of thin sections
analyzed from different lithostratigraphic units in the Tripoli-Gabes Basin.
Fig 2.1 Lithostratigraphic
nomenclature used in this study (After Fournie, 1978).
Fig 2.2 A chart showing the
lithostratigraphic nomenclature employed for the Tripoli-Gabes Basin (Tunisian)
as compared to Sirt Basin (Libyan) Stratigraphy.
Fig 2.3 Schematic chart showing the
relationship between the International chronos-tratigraphic divisions and the
lithostratigraphy of the study area and immediate onshore of Libya and Tunisia.
Fig 2.4 The Phanerozoic
chronostratigraphic scheme used in this study (After Harland et al.,
1982).
Fig 2.5 Comparison between the lithostratigraphic
nomenclature of the Metlaoui Group proposed by previous workers and the new
scheme adopted in this study.
Fig 3.1a Movement of Africa relative
to Europe since the Early Mesozoic derived from Atlantic magnetic anomaly data.
Dashed line: according to pitman and Talwany (1972) and Dewey et al.
(1973). Full line: modification made by Biju-Duval et al.(1977).
(Numbers are ages in millions of years).
Fig 3.1b Relative motion history of
Africa, Iberia with respect to Eurasia from Early Jurassic to present time.
Oblique Mercator projection with North Pole at 50 N, 155W. Position of
continents at 190 Ma. Stages in Ma. Present latitudes and longitudes every 10
on continents. Interpolated flow-line: continuous lines. Pole positions
describing motion of Africa with respect to Eurasia from stage to stage are
also shown (circles connected by dashed lines with parameters of Savostin and
others, 1985). (After Le-Pichon et al., 1986).
Fig 3.2 Simplified plate tectonic scheme during
three stages (a: 190 Ma, b: 155 Ma, c: 130 Ma). Relative motion vectors in
centimeters per annum. Positions of poles of rotation of plates shown with
respect to Eurasia from Previous stage, Africa (AF), Iberia (IB). Schematic
plate boundaries indicated by continuous line; open triangles, oceanic
subduction; closed triangles, continental collision; double dotted line,
oceanic accretion; hatched pattern, oceanic crust; dotted pattern, thinned
continental crust. (After Le-Pichon et al., 1986).
Fig 3.2 (contd.) Simplified tectonic scheme
during three stages (d: 110 Ma, e: 80 Ma, f: 65 Ma).
Fig 3.2 (contd.) Simplified plate tectonic
scheme during three stages (g: 35 Ma, h: 20 Ma, i: 10 Ma).
Fig 3.2 (contd.) Present day position of continents.
Fig 3.3 Physiographic diagram of the
Mediterranean (Heezan and Thorpe, 1970: Lamont-Doherty Geological Observatory).
Fig 3.4 Map of western Mediterranean
area showing major geological features. (After Biju-Duval et
al., 1974).
Fig 3.5 Map of the eastern Mediterranean
area showing major geological features. (After
Biju-Duval et al., 1974).
Fig 3.6 Age and distribution of the
Mediterranean basins: 1. Mesozoic and Lower Tertiary mainly carbonate platform.
2. Mesozoic and Lower Tertiary presumed pelagic sediments along Alpine belt
foredeep. 3. Front of Nappe. 4. Limit
of the thick salt basins. 5. Main Tertiary to present deltas. 6. Oligocene and
younger basins. 7. Miocene and younger basins. 8. Upper Miocene-Pliocene basins.
9. Minimum thickness of post-tectonic sediments. 10. Alpine folded belts (After
Byramjee et al., 1975).
Fig 3.7 The main tectonic elements
of the Pelagian platform (modified from tectonic map of Libya by: Agip
(N.A.M.E).
Fig 3.8 Bathymetry map of southwest central
Mediterranean. Contours in meters, (modified from Awar and Missallati, 1981).
Fig 3.9 Composite display of the
tectonic evolution of the Pelagian Platform. (After Benelli et al.,
1985).
Fig 3.10 Moho depth map derived from
the results of the European geotraverse. (After Ben- Ferjani et al.,1990).
Fig 3.11 Surface and subsurface
igneous occurrence in the Pelagian Platform and surrounding regions.
Fig 4.1 Base map with well location
used in this study (Longitude is East of Greenwich).
Fig 4.2 Isopach map of the Zebbag
Formation (thickness and contours are in metres).
Fig 4.3 Diagram showing the
penetrated section of the Zebbag Formation across the basin from south to north
(Lithological symbols are given in fig.1.6).
Fig 4.4 Isopach map of the Kef
Formation (thickness and contours are
in metres).
Fig 4.5 Diagram showing the
penetrated sections of the Kef Formation across the basin.
Fig 4.6 Isopach map of the Abiod
Formation (thicknesses and contours are in metres).
Fig 4.7 Diagram showing the
penetrated sections of the Abiod Formation across the basin.
Fig 4.8 Isopach map of the
Maastrichtian El-Haria A Member (thicknesses and contours are in metres).
Fig 4.9 Diagram showing the penetrated
sections of the EL-Haria Formation (A and B members) across the basin.
Fig 4.10 Isopach map of the Paleocene
EL-Haria ‘B’ Member (thicknesses are computed from seismic data).
Fig 4.11 Isopach map of the Ypresian
Metlaoui Group (thicknesses are computed from seismic data).
Fig 4.12 Eocene subcrop
map.
Fig 4.13 Map showing the vertical and
lateral relationship between the Metlaoui Group Formations.
Fig 4.14 Isopach map of the Chouabine
Formation (thicknesses and
contours in metres).
Fig 4.15 Diagram showing the
penetrated section of the Metlaoui Group across the basin.
Fig 4.16 Diagram showing the
penetrated section of the Metlaoui Group in an east-west direction.
Fig 4.17 Lithofacies map of the
Chouabine Formation.
Fig 4.18 Isopach map of the Jirani
Formation.
Fig 4.19 Lithofacies map of the Jirani
Formation.
Fig 4.20 Isopach map of the EL-Garia
Formation.
Fig 4.21 Lithofacies map of the
EL-Garia Formation.
Fig 4.22 Map showing the vertical and
lateral relationship between the Upper/Middle Eocene sequences.
Fig 4.23 Diagram showing the
stratigraphic relation -ship between the Upper/Middle Eocene sequences across
the basin.
Fig 4.24 Isopach map of the Upper/Middle
Eocene sequence (Cherahil, Reinech Members and Souar Formation).
Fig 4.25 Complete Bouger gravity map
of the study area.
Fig 4.26 Gravity (a), and Magnetic
(b) profiles across the basin (for profile location see fig. 4.25 and
fig. 4.27).
Fig 4.27 Total field magnetic
intensity map of the study area.
Fig 4.28 Multichannel depth seismic
profile (WT-84-28) and line drawing of the same line (for location see fig.
1.5).
Fig 4.29 Multichannel depth seismic
profile (WT-84-10) and line drawing of the same line (for location see fig.
1.5).
Fig 4.30 Multichannel depth seismic
profile (WT-84-30) and line drawing of the same line (for location see fig.
1.5).
Fig 4.31 Multichannel depth seismic
profile (WT-84-13/1) and line drawing of the same line (for location see fig.
1.5).
Fig 4.32 Multichannel depth seismic
profile (WT-84-13/2) and line drawing of the same line (for location see fig.
1.5).
Fig 4.33 Multichannel depth seismic
profile (WT-84-06) and line drawing of the same line (for location see fig.
1.5).
Fig 4.34 Multichannel depth seismic
profile (WT-84-15) and line drawing of the same line (for location see fig.
1.5).
Fig 4.35 Multichannel depth seismic
profile (WT-84-22) and line drawing of the same line (for location see fig.
1.5).
Fig 4.36 Location map of the deep
seismic line RS-86-01.
Fig 4.37 Multichannel, deep seismic
profile (RS-86-01) and line drawing of the same line.
Fig 4.38 structure contour map of
base Tertiary unconformity (data computed from seismic and contour interval = 250
m).
Fig 4.39 structure contour map of of
the Metlaoui Group (data from seismic and contour interval = 100 m).
Fig 4.40 Map showing the
main salt structures the basin as interpreted seismic data.
Plate 4.1 Dolomudstone with anhydrite
filling micro-fractures. (Zebbag Formation, M1-NC41 at 3566.8m, XN, X25).
Plate 4.2 Aphanitic mosaic of
anhydrite crystals filling collapse fractures in dark brown Dolomudstone.
(Zebbag Formation, M1-NC41 at 3566.8, XN, X16).
Plate 4.3 Microfabric composed of
alternating laminae of Planktonic forams and dark pelagic mudstone. (Kef
Formation, M1-NC41 at 3102m, PPL, X25).
Plate 4.4 Enlarged view of part of
Plate 4.3 (upper) showing details of planktonic forams and framboidal pyrite in
brown lime-mudstone (note all forams chambers are occupied by a single crystal
of clear calcite). (PPL, X40).
Plate 4.5 Planktonic and small
Benthonic forams in a laminated dark grey argillaceous wackestone. (Abiod
Formation, J1-NC41 at 1764.2m, PPL, X63).
Plate 4.6 Enlarged view of part of Plate
4.5 (above) showing a single Globotruncana embedded in a dark grey
argillaceous wackestone. (PPL, X100)
Plate 4.7 Dolomitic argillite mudstone
with bands of bituminous material displaying microflame structures. Scattered
globigrinid & dolomite rhombs and abundant pyrite abundant. (EL-Haria A
Mbr., C1-NC41 at 2943.5m, PPL,X40).
Plate 4.8 Rotaliid foraminifer in
laminated brown shale. The foram is
almost filled in by pyrite except for the core of the chambers, which contain
authigenic chert. (El-Haria ‘A’ Mbr; C1-NC41 at 2948.7m, PPL, X200).
Plate 4.9 Recrystallized planktonic
forams embedded in a microfabric of sparry calcite mosaic. (El-Haria ‘B’ Mbr;
C1-NC41 at 2791.1m, PPL, X400).
Plate 4.10 Anhydrite nodules that have
suffered compaction enclosed by very dark (opaque) dolomite. (Chouabine Fm., A2-NC41 at 2828m, XN, X25).
Plate 4.11 Detailed view of a single
anhydrite nodule (top), it exhibits rosette texture formed by stacked laths
with radiating habit. (XN, X100).
Plate 4.12 Bioclastic packstones with
diverse allochem including abundant oyster fragments. Detrital quartz grains are common. (Chouabine Fm., A2-NC41 at 2807.5m, XN, X100).
Plate 4.13 Extensive micritization of
mulluscan bivalve fragment by endolithic organisms. (Chouabine Fm., A2-NC41 at 2807.5m, PPL, X200).
Plate 4.14 Oolitic grainstone texture
showing poorly preserved microfabric.
Nuclei of micrite clasts and fine skeletal debris. (Chouabine Fm., C1-NC35A at 2963.6m, PPL,
X100).
Plate 4.15 Bolivina and planktonic
organisms floating in lithoclastic texture.
(Chouabine Fm., B3-NC41 at 2694.8m, PPL, X160).
Plate 4.16 SEM micrograph showing
primary pore space in nummulite grain surrounded by dense mudstone. This type of porosity cannot form good
reservoir rock. (Chouabine Fm., B2-NC41
at 2613.1m).
Plate 4.17 SEM micrograph of wholly
recrystallized planktonic test enclosed in clay matrix (illite). (Chouabine
Fm., B3-NC41 at 2694.8m).
Plate 4.18 Partially dolomitized
peloidal grainstone. Peloids appear
resistant to dolomitization resulting in a poor intergranular porosity. (Jirani Fm., C2-NC41 at 2658.8m, PPL, X100).
Plate 4.19 Dolomitized bioclastic
wackestone with relics of skeletal allochems preserved as enlarged vuggy
porosity. (Jirani Fm., B2-NC41 at
2583.5m, PPL, X25).
Plate 4.20 Completely dolomitized
bioclastic packstone. The dolomite
occurs in two forms; a) matrix replacement mosaic and b) partially outlining
skeletal molds. (Jirani Fm., B2-NC41 at 2583.5m, PPL, X200).
Plate 4.21 Enlarged view of part of
Plate 4.20 (upper) showing the second generation of dolomite. It is unimodal, coarse, rhombohedra and
partially blocks moldic pore spaces. (PPL, X400).
Plate 4.22 SEM micrograph showing a
planar rhombohedral dolomite mosaic with good intercrystalline porosity. Hydrocarbon substance appears as ghost
around many crystals. (Jirani Fm.,
B3-NC41 at 2583.8m).
Plate 4.23 Close-up of Platte 4.22
displays the intercrystalline porosity in relation to the dolomite rhombs.
Plate 4.24 Bioclastic wackestone
containing echinoid and oyster fragments.
Note the upper echinoid fragment with authigenic quartz filling pore
spaces. (El-Garia Fm., A2-NC41 at
2795m, XN, X25).
Plate 4.25 Dolomitic lime-clast
packstone exhibits extensive wispy seams rich in insoluble pyrobitumens
residue. (El-Garia Fm., H1-NC41 at
3374.8m, PPL, X320).
Plate 4.26 Molluscan bivalves defined
by thin micrite envelope and neomorphic drusy spar calcite replacing original
aragonite. (El-Garia Fm., C1-NC35A at 2640.5m,
PPL, X63).
Plate 4.27 Dolomitized mudstone
texture showing a polymodal rhombohedral dolomite mosaic. Note the intercrystalline pore spaces
(white). (El-Garia Fm., C1-NC41 at
2545.1m, PPL, X1000).
Plate 4.28 Syntaxial overgrowth around
echinoid spine in a bioclastic wackestone. (El-Garia Fm., B3-NC41 at 2446.4m,
XN, X320).
Plate 4.29 Bioclastic packstone that
displays partial dissolution of nummulite grain and its surroundings filled
later by hydrocarbons (black). (El-Garia Fm., B3-NC41 at 2446.4m, XN, X100).
Plate 4.30 Nummulites and echinoid
fragment enclosed in a poikiloptic cement mosaic. (El-Garia Fm., B3-NC41 at 2446.4m, XN, X100).
Plate 4.31 Nummulite grain exhibits
partial micritization and subsequent cementation by fine equant mosaic
calcite. (El-Garia Fm., B3-NC41 at
2477.1m, PPL, X25).
Plate 4.32 Nummulite packstone showing
deformation due to burial compaction and subsequent cementation by blocky
calcite mosaic. (El-Garia Fm., B3-NC41
at 2543.9m, PPL, X25).
Plate 4.33 Bolivina with unidentified
planktonic forams embedded in a nummulithoclastic texture. (El-Garia Fm., B2-NC41 at 2517.4m, PPL,
X63).
Plate 4.34 SEM micrograph showing
drusy scalenohedral calcite cement lining the interior or a nummulite chamber.
Note the preserved primary porosity.
(El-Garia Fm., C1-NC35A at 2628.3m).
Plate 4.35 Coarse calcite crystal and
clusters of authigenic clay platelets reduce the primary porosity within a
nummulite chamber. (Compare with the
top micrograph). (El-Garia Fm., B3-NC41
at 2557.7m).
Plate 4.36 SEM micrograph showing a
fine equant calcite mosaic covering the chambers and septae inside a nummulite
test. Intragranular porosity is largely
unaffected. (El-Garia Fm., B3-NC41 at 25577.7m).
Plate 4.37 Close-up view of the top
micrograph showing crystal details.
Note the intercrystalline pore spaces.
Plate 4.38 Single crystal of crinoid
ossicle with characteristic central canal with other molluscan debris embedded
in dark, cloudy lime-mud. (Cherahil ‘A’
Mbr., P1-NC41 at 2484.2m, PPL, X63).
Plate 4.39 Foliated calcite structure
of oyster shell fragment which is a major skeletal constituent of the Cherahil
‘A’ Member. (A2-NC41 at 2462.8m, XN,
X100).
Plate 4.40 Authigenic quartz (chert)
filling borings in molluscan bivalve shell, probably oyster. (Cherahil ‘A’, A2-NC41 at 2463.7m, XN, X63).
Plate 4.42 Hand specimen comprising nummulitic
packstone displaying well-preserved and well-sorted nummulites in lime
mudstone. Note the excellent
preservation of intragranular porosity.
(Reinech Member, F2-NC41 at 2411.9m, sample width is 5cm).
Plate 4.43 Bivalve fragments in
dark-grey lime-mud matrix. Note the
solution enlarged pore spaces. (Reinech Member, K1-NC41 at 2577.7m, XN, X25).
Plate 4.44 Original aragonite skeleton
of bivalve shells altered to calcite by complete dissolution and later
infilling of the leached void.
(Cherahil ‘B’ Member, F2-NC41 at 2219.9m, XN, X160).
Plate 4.45 Crinoid ossicle with
bioclast fragment embedded in original mud matrix that has been completely
obliterated by recrystallization. Note
the irregular stylolite seam across the sample. (Cherahil ‘B’ Member, C1-NC35A at 2186.4m, PPL, X320).
Plate 4.46 Pyritic globigrinid
shale. Note the blocky calcite cement
that occupies most of the skeletal cavities. (Souar Fm., B3-NC41 at 2445.1m,
PPL, X400).
Plate 4.47 Bolivinidis in dolomitic
laminated shale. Framboidal pyrite is
abundant and seen here infilling foram chambers. (Souar Fm., B3-NC41 at
2429.6m, XN, X400).
Fig 5.1 Schematic diagram of reconstructed (loaded)
sedimentary section and backstripped (unloaded) sedimentary section. (After Steckler and Watts, 1978).
Fig 5.3 Uncorrected burial history curves (top) and
curves corrected for compaction (bottom) for the same well: F1-NC41.
Fig 5.4 Sedimentation rate plot versus time. Solid
line represents sediments uncorrected for compaction. Dotted line represents decompacted sedimentation rates. (Well: F1-NC41).
Fig 5.5 Biostratigraphic zonation scheme for the Tripoli-Gabes
Basin as proposed by Duronio, 1985.
Fig 5.6 Paleobathymetry data for well C1-NC35A
(after Cococcetta, 1981).
Fig 5.7 Calculated basement subsidence curves at
different localities across the basin.
Fig 5.8 Schematic diagram showing the principal
features of the stretching model of McKenzie (1978). a) Initial conditions showing the lithosphere (including a crust)
in thermal equilibrium. b) Uniform
extension during which the lithosphere is extended and thinned. Since isostatic equilibrium is assumed, the
extension is associated with an initial subsidence that depends on the initial
crustal thickness assumed. c) Cooling
following the extension at the hot asthenosphere cools. The cooling is associated with a thermal
subsidence, which decays exponentially with time (After Watts, 1981).
Fig 5.9 Theoretical subsidence curves based on
McKenzie’s (1978) model for different values of stretching factor Beta.
(Calculation was made assuming a 125km lithosphere and a 35km crust).
Fig 5.10 Comparison between the
burial history curves (correct and uncorrected for compaction) and the tectonic
subsidence curve (backstripped) at the example well F1-NC41.
Fig 5.11 Comparison between the
predictive subsidence model (Beta) and the calculated tectonic subsidence
curves at the southern margin of the basin (see legend for well location).
Fig 5.12 Comparison between the
predictive subsidence model (Beta) and the calculated tectonic subsidence
curves at the central parts of the basin (see legend for well location).
Fig 5.13 Comparison between the
predictive subsidence model (Beta) and the calculated tectonic subsidence
curves at the central parts of the basin (see legend for well location).
Fig 5.14 Comparison between the
predictive subsidence model (Beta) and the calculated tectonic subsidence
curves at the northern margin of the basin (see legend of well location and
compare with Fig. 5.11).
Fig 5.15 Basement subsidence map for
the time interval 83-73 my (Campanian).
Fig 5.16 Basement subsidence map for
the time interval 73-54.9 my (Maastrichian/ Paleocene).
Fig 5.17 Basement subsidence map for
the time internal 54.9 – 50.5 my (Ypresian).
Fig 5.18 Basement subsidence map for
the time interval 50.5-38 my (Upper/Middle Eocene).
Fig 5.19 Basement subsidence map for
the time interval 38-24.6 my (Oligocene).
Fig 5.20 Basement
subsidence map for the time interval 24.6-14.4 my (Lower Miocene).
Fig 5.21 Basement subsidence map for
the time interval 14.4-11.3 my (Middle Miocene).
Fig 5.22 Basement
subsidence map for the time interval 11.3-5.1 my (Upper Miocene).
Fig 5.23 Cumulative
basement subsidence map at 54.9 my (Datum = Base Tertiary).
Fig 5.24 Cumulative
basement subsidence map at 50.5 my (Datum = Base Tertiary).
Fig 5.25 Cumulative
basement subsidence map at 38 my (Datum = Base Tertiary).
Fig 5.26 Cumulative
basement subsidence map at 24.6 my (Datum = Base Tertiary).
Fig 5.27 Cumulative
basement subsidence map at 14.4 my (Datum = Base Tertiary).
Fig 5.28 Cumulative
basement subsidence map at 11.3 my (Datum = Base Tertiary).
Fig 5.29 Cumulative
basement subsidence map at 5.1 my (Datum = Base Tertiary).
Fig 6.1 Correction curve
for log temperature readings (modified from Hood et al., 1975).
Fig. 6.2 Temperature gradient plot
for Well C2-NC41. Note the difference
between the log and the corrected temperatures and the close relationship
between the corrected and the test recorded borehole temperatures.
Fig 6.3 Average geothermal gradient map for the
study area (oC/100m).
Fig 6.4 Plots of the observed thermal maturity
values (TAI) for eight wells in the basin using the Lower Eocene top as a datum
line. Note the uniform trend of the
observed maturities.
Fig 6.5 TAI/Ro relationship graph as suggested by
Agip, (1985).
Fig 6.6 Decompacted
burial history curves (a), observed (b) and predicted maturities (c) at A1-NC41
well.
Fig 6.7 Location map of the eight wells used to
derive organic maturity data for the basin.
Fig 6.8 Relationship between (TA1/Log TTI) at eight
wells in the basin. The best square fit
line represents the equation: TA1 = 0.3132 + 0.49705 (Log TTI).
Fig 6.9 a) Decompacted burial history,
b) observed maturity and c) predicted maturity at A1-NC41
(compare the maturities in this figure with that of Fig. 6.6).
Fig 6.10 a) Decompacted burial history,
b) observed maturity and c) predicted maturity at B1-NC41.
Fig 6.11 a) Decompacted burial history,
b) observed maturity and c) predicted maturity at B2-NC41.
Fig 6.12 a) Decompacted
burial history, b) observed maturity and c) predicted maturity at
C1-NC41.
Fig 6.13 a) Decompacted
burial history, b) observed maturity and c) predicted maturity at
C2-NC41.
Fig 6.14 a) Decompacted
burial history, b) observed maturity and c) predicted maturity at
D2-NC41.
Fig 6.15 a) Decompacted
burial history, b) observed maturity and c) predicted maturity at
F1-NC41.
Fig 6.16 a) Decompacted
burial history, b) observed maturity and c) predicted maturity at
H1-NC41.
Fig 6.17 Organic maturity of the
Abiod Formation referred to the end of the Miocene.
Fig 6.18 Organic maturity of the
Abiod Formation referred to the present time.
Fig 6.19 Sedimentation rate map of
the Abiod Formation (cm/1000y).
Fig 6.21 Organic maturity of the
El-Haria Formation referred to the present time.
Fig 6.22 Sedimentation rate map of
the El-Haria Formation (cm/1000y).
Fig 6.23 Organic maturity of the
Metlaoui Group referred to the end of the Miocene.
Fig 6.24 Organic maturity of the
Metlaoui Group referred to the present time.
Fig 6.25 Sedimentation rate map of
the Metlaoui Group (cm/1000y).
Table 6.1 Comparison between the
DST/PT recorded temperatures and those obtained by correcting log recorded BHT
according to Fertl-Wichmann (1977) and Hood et al., (1975).
Table 6.2 Calculated static formation
temperature versus depths of the wells studied.
Table 6.3 Measured thermal alteration
index (TAI) for eight wells in the Tripoli-Gabes Basin.
Table 6.4 Temperature factors for
different temperature intervals (after Waples, 1980).
Table 6.5 Maturation values obtained
by Lopatin modeling at different sites based on present time and tat the end of
the Miocene and sedimentation rates.
Fig 7.1 The three principal models normally invoked
to explain the origin of major evaporite basins. a) The shallow basin-shallow
water model which requires basinal subsidence to account for thick evaporite
deposits; b) the deep basin-deep water model, with influx taking place in a
less dense brine layer above a deep, denser brine layer; c) the deep basin-shallow
water model (or deep desiccating basin), with shallow evaporites forming far
below normal sea level (after Jenyon, 1986).
Fig 7.2 A model for deep-water evaporite deposition.
Four stages in the filling of such a basin are shown (after Schmalz, 1969).
Fig 7.3 Postulated patterns of evaporite
distribution. (A) The bull’s-eye
pattern is typical of deposition in completely enclosed basins. (B) The teardrop pattern is typical
of deposition in restricted basins.
Fig 7.4 Sketch map of possible Triassic facies
distribution (after Salaj, 1978).
Fig 7.5 Salt structures and their distribution in
the Tripoli-Gabes Basin (Agip, 1990).
Fig 7.6 Salt movements as studied in three wells
within the basin.
Table 7.1 Order of precipitation from
sea-water (After Schreiber and Marshak, 1981).
Fig 8.1 The type section of the Metlaoui Group at
B2-NC41 as defined by Hammuda et al., (1985).
Fig 8.2 Schematic diagram showing the relationship
between the global sea level curve and sediments of the El-Haria, Metlaoui
Group and Souar Formation.
Fig 8.3 Depositional model for the Chouabine
Formation (modified from Read, 1982).
Fig 8.4 Dolomitization by seepage refluxion model as
suggested by Adams and Rhodes, (1960).
Fig 8.5 Depositional model for the El-Garia
Formation (modified from Moody and Grant, 1989).
Fig 8.6 The main diagenetic features and
environments of the El-Garia Formation.